3 Answers
3

Sadly the Meissner effect can't be used as an anti-gravity device. If you lay under the magnet and put the 3mm superconducting disk and car on top you would indeed be squished.

The presenter does use the words "in my hand", but I suspect this is just poor phrasing and I'm sure he is not suggesting he could lift a car in one hand using a superconducting disk. What he means is simply that the repulsion between the magnet and the superconducting disk is so strong that you would need to press with a force of 1000kg to push the disk into contact with the magnet. That force is of course transmitted to whatever is underneath the magnet e.g. a squished physicist.

I see what you mean about how it's not anti-gravity, but it is validly levitation, right? The proposition of anti-gravity as you've addressed it is a violation of equal and opposite forces. I think the practical problem with levitating cars is the separate issue of needing strongly magnetized roads.
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Alan RomingerJul 3 '12 at 13:57

"That force is of course transmitted to whatever is underneath the magnet e.g. a squished physicist." – No, this does not sound correct. the superconductor is fixed i place relative to a magnetic field. it's not simply 'pushed' up, and the force 'lifting' would not act on a person underneath, squashing her, like a rocket engine blowing downwards.
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mikkelbreumDec 22 '12 at 23:24

@mwb: the superconducting disk and the car together form a system with the force between them stopping the card and disk from approaching each other too closely. But if you consider the disk and car as a single system it obviously has a mass, and will accelerate in a gravitational field. If you pushed the disk/car system off a cliff it would fall to the bottom. This is why I say if you were under the disk/car system you would feel a downwards force of $mg$ where $m$ is the mass of the disk+car i.e. mostly the mass of the car.
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John RennieDec 23 '12 at 7:24

of course, I misread it, as if the physicist was between the magnet and the disc, but you did in fact say, that the physicist was under the magnet.
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mikkelbreumJan 4 '13 at 16:03

The Title of the video is misleading. What Boaz Almog is demonstrating is not at all levitation. The disk is not pushed away from the magnet, and it does not levitate. It is fixed or trapped in the magnetic field, by an effect refered to as "Quantum Locking" or "Flux Pinning". This can be demonstrated by locking the disk in space underneath the magnet, which works just as well. If the magnet was pushing, – and so 'levitating' – the disk, it would be a force acting upon the disk to neutralize the gravitational pull from earth, and it would not be possible to fix the disk under the magnet (it would fall down to earth).

The disc is essentially a very thin superconductor. Superconductors will expel magnetic fields from within, but in this case, where the superconductor is so thin, millions (or billions) of single magnetic strands penetrates the disk, allowing for the disk to be locked in place at various distances and angles from the magnet.

The disk is able to carry the cooling material put on top of it (and can carry 70.000 times it's own weight), but to scale the disk up wouldn't simply be a matter of making it thicker (I believe the magnetic strands would no longer penetrate the superconductor). Maybe this can be achieved by layering many super thin discs?

Anyway, say that the experiment could be scaled up, to carry a car, then no, the person underneath would not be crushed – no more than you're crushed by a bridge, walking under it, as it's fixed in place. And you wouldn't really "lift the car" with the hand - no more than you're lifting a bridge, by placing you hand under it pressing up. You can't lift it, and if the experiment had been scaled up to this level, you would also not be able to displace the locked super conductor (with or without a car on it) with the strength of your arm.

I highly doubt, that a superconductor can support 70,000 times its own weight.
In fact, the force generated to "levitate" the disc is equal to the weight of the superconductor.
These properties are attributed to a magnet, which a superconductor is not.